The present invention relates with control of mechanical devices by means of electric signals produced by muscular contraction, and more particularly to a system and method for acquiring signals produced by muscular electrical activity at the outer surface level of the human epidermis, in order to control an arm prosthesis.
Nowadays, there are mechanical systems controlled by electric signals produced by muscular contraction, and can be find in many different applications. Electromechanical prosthesis responds in a precise way to the muscular stimulation of patients who have been lost a fractional of a superior member (either congenital or resulting from a surgery).
Conventional prosthetic arms working with corporal movements and depend of said corporal movements to manipulate wires that are controlling the prosthesis. Myoelectric prosthesis are controlled by electrical signals transmitted from inferior muscles to the epidermis, this signals are amplified and are sent to microprocessors that activate motors disposed in joints and hands
If a muscle is contracted it produces an electrical signal due to depolarization of membranes of muscular fibers. Each cell gives a small voltage quantity, which together are converted in a sufficient significant signal so it can be captured by an electrode and thus be brought to a signals processing system.
As signal has a voltage level of a few millivolts, is necessary to make an electronic amplification in order to make any kind of processing, that it must be do in a similar way.
Any signal (particularly a biological signal) can be submitted to a huge variety of processing in order to obtain useful information from it, among which are: filtrated to remove unwanted frequency components, levels detection, determination of frequency spectrums, integration, derivation, among others. These processes can be carried out either analogically or digitally.
Given that digital systems are more adaptable and (many times) more efficient than analog systems, the employment of computers programs is the most appropriated.
There are many systems that can be used in order to produce movement like response to electric stimulus, such as, servomotors, stepper motors and direct current motors.
Generally in known systems are used different muscular areas in order to obtain any movement of the prosthesis, that is to say, it use readings of antagonist muscle contraction to make opposite movement, for example, open hand movement is carried on when there are biceps contraction, and close hand movement is carried on when there are triceps contraction, both are antagonist muscles, and carrying with the use of multiple electrodes.
In view of the above, is advantageous to have a myoelectric data acquisition system to control efficiently and simple the movements of a prosthesis, using a pair of electrodes to make the contraction readings, therefore is an objective of the invention provide a system for amplify, filtering and digitalizing myoelectric signals, in order to control an arm prosthesis, wherein is only used a pair of electrodes to detect signals to produce all the prosthesis movements.
Another objective of invention is to provide a system with many freedom degrees, capable of controlling the open and close hand movements, pronation and supination of forearm, flexion and extension of arm prosthesis.
Still another objective of the invention to provides a system that using muscular contraction time in order to controlling arm prosthesis movements.
The myoelectric data acquisition system and arm prosthesis control according present invention includes a pair of copper electrodes disposed on the best muscle area according patient amputation and a copper electrode away of said area, said electrode works like a biological ground. Due myoelectric signal is given in microvolts, it requires of amplification stage and conditioning of said signal in order to be processed and interpreted, so that a diversity of mechanicals movements are generated for the prosthesis according patient necessities in a simply and efficient way, only with alimentation of a 12 volts battery.
The system can be divided in two blocks, conditioning of myoelectric signal through operational amplifiers and analogue circuits, and digital control systems through a micro controller who has analog comparator, ND converter and drivers.
Invention provides a myoelectric data acquisition system in order to controlling an arm prosthesis, comprising: a pair of electrodes disposed in a muscle, in a residual piece of a person amputated arm, in order to detect myoelectric signals, and an electrode disposed in said residual arm piece, said electrode is move away of said pair electrodes and works like a ground, myiolectric signal conditioning means, and processing control prosthesis means which receive conditioned signals from conditioning means, wherein processing control prosthesis means: comparing means to evaluate muscular contraction time and muscular contraction voltage with threshold time and threshold voltage respectively activating means for activating at least a motor, said motor produce a predetermined movement of the prosthesis in response to an activation signal which is sent from comparing means, wherein the electrodes provides the myolectric signal to activating different movements of the prosthesis, without changing electrodes to another muscle.
Activating means produces the activation of a motor to open a hand of the prosthesis, when the comparing means sends the activation signal, if the muscular contraction time is longer than the threshold time and the muscular contraction voltage is higher than the threshold voltage
When the comparing means sends the activation signal, because the muscular contraction time is longer than the threshold time and the muscular contraction voltage is lower than the threshold voltage, activating means produces the activation of a motor to close the hand of the arm prosthesis. Activating means produces an activation motor to flex the arm prosthesis, when means to compare send the activation signal, if the muscular contraction time is lower than the threshold time, muscular contraction voltage is higher than the threshold voltage and the time between two muscular contractions is longer than 400 ms.
When comparing means sends an activation signal, due that the muscular contraction time is lower than the threshold time, the muscular contraction voltage is lower than the threshold voltage and the time between two muscular contractions is longer than 400 ms, activating means produces the activation of a motor to extend the arm prosthesis.
Activating means produces the activation of a motor for the pronation of a forearm prosthesis, when comparing means sends the activation signal, when comparing means sends the activation signal, if the muscular contraction time is lower than the threshold time, the muscular contraction voltage is higher than the threshold voltage and the time between two muscular contractions is lower than 400.
Activating means produces the activation of a motor for the supination of a forearm prosthesis, when comparing means sends the activation signal, if the muscular contraction time is lower than the threshold time, the muscular contraction voltage is lower than the threshold time and the time between two muscular contractions is shorter than 400 ms.
Also the invention provides a method of myolectric acquisition and processing signals to control an arm prosthesis that consists in the following: detection of signals with a pair of electrodes placed in a muscle of a residual part of an arm that has been amputated of a person, and an electrode placed in a residual part of the arm away of the pair of electrodes functioning as ground; conditioning the signals to obtain a voltage value of muscular contraction; compare the muscular contraction time and the muscular contraction voltage with the threshold time and the threshold voltage, respectively; activating at least a motor to produce a predetermined prosthesis movement, in response to an activation signal; wherein to produce different movements of the prosthesis, the previous stages are repeated, without placing the electrodes in another muscle.
The activation of a motor to open a hand of the prosthesis, is produced when the comparing means sends the activation signal, if the muscular contraction time is longer than the threshold time and the muscular contraction voltage is higher than the threshold voltage.
The activation of a motor to close a hand of the prosthesis, is produced when the comparing means sends the activation signal, if the muscular contraction time is longer than the threshold time and the muscular contraction voltage is lower than the threshold voltage.
The activation of a motor to flex the arm prosthesis, is produced when the means to compare sends the activation signal, if the muscular contraction time is shorter than the threshold time, the muscular contraction voltage is higher than the threshold voltage and the time between two muscular contractions is longer than 400 ms.
the activation of a motor to extend the arm prosthesis is produced, when the means to compare sends the activation signal, if the muscular contraction time is shorter than the threshold time, the muscular contraction voltage is lower than the threshold voltage and the time between two muscular contractions is longer than 400 ms.
The activation of a motor for the pronation of a forearm of the prosthesis, is produced when the means to compare sends the activation signal, if the muscular contraction time is shorter than the threshold time, the muscular contraction voltage is higher than the threshold voltage and the time between two muscular contractions is shorter than 400 ms.
The activation of a motor for a supination of a forearm of the prosthesis, is produced when the means to compare sends the activation signal, if the muscular contraction time is shorter than the threshold time, the muscular contraction voltage is lower than the threshold voltage and the time between two muscular contractions is shorter than 400 ms.